Motorcycles and certain other motor vehicles, by their very nature, have fuel system components which are exposed to damage by collision to a much greater degree than most other on-road vehicles. Since the fuel system components, and especially the fuel tank, are exposed to possible collision damage and are in close proximity to the rider, it is desirable to reduce the risk resulting from fuel loss from the fuel system due to collision.
The conventional mounting location for the fuel tank on a motorcycle is directly in front of the rider. Since a frontal impact is the most common type of motorcycle collision, rider ejection toward the front of the vehicle is common. This sometimes results in impact between the rider and the fuel tank. In addition, fuel can be forced toward the front portion of the fuel tank during a collision due to rapid deceleration of the vehicle.
Motorcycle fuel tanks commonly have fuel filler caps having a vent and a relief valve. The relief valve, which is designed to open at low pressure, prevents internal tank pressure from increasing due to heat, pressure surges resulting from deceleration, or fuel tank deformation resulting from collision with another vehicle or a fixed object or contact with the rider during collision or ejection. Thus, when pressure increases within the tank, fuel often exits the filler cap through the pressure relief valve. If the increase of pressure within the fuel tank is due to a front end collision, the ejection path of the motorcycle rider often passes through the fuel exiting the fuel tank through the pressure relief valve located in front of the rider.
The discharge of fuel onto the rider during an accident increases the risk that the rider will be burned if the fuel lost from the tank catches fire. The risk of fire is increased by the fact that the fuel tank is often located directly above hot engine parts and near electrical components.
Some motorcycle engine-frame configurations have a fuel tank which is positioned below the rider, where it is partially protected by the motorcycle frame. If these tanks are crushed, fuel may also be directed through the filling cap pressure relief valve upwardly toward the rider.
The vent on the fuel filler cap helps to maintain atmospheric pressure inside the tank as fuel is consumed during use of the motorcycle. Many existing vent designs also, however, allow fuel to flow outwardly from the tank when the vehicle falls onto its side, or when internal fuel tank pressure rises.